Ray et al U.S. Pat. No. 2,628,010 discloses a machine for alternately moving a pair of conveyors, including an air cylinder for alternately actuating a pair of ratchets adapted to rotate respective shafts each carrying a gear operatively connected to a series of gears and further shafts carrying the end sprockets for engagement with the chains of the pair of conveyors.
Natalis U.S. Pat. No. 2,857,787 discloses a common drive mechanism for a pair of asynchronously intermittent, rotating turrets, wherein a portion of the kinetic energy of one turret undergoing deceleration is transferred to the other turret undergoing acceleration. A drive shaft is connected to the two turrets by a pair of cams. A motor is connected to a first speed reduction unit which, in turn, is connected to a second worm gear speed reduction unit, the output of which is connected by a chain to the drive shaft.
Oprecht U.S. Pat. No. 4,354,086 discloses a drive motor driving two separate cam drive gears for driving first and second transport devices via respective sprocket wheels.
Ljungstrom et al U.S. Pat. No. 4,790,123 discloses a method and machine for driving a pair of conveyors asynchronously. The machine includes a motor, an indexing gear box operatively connected to the motor to convert the continuous rotation of the motor to an indexing movement and to transfer the movement to a driving shaft located centrally in the machine and which, in turn, drives two parallel conveyors.